Urea is a nitrogen-containing chemical product that is used in many industries, including the agricultural, automotive, medical, biochemical, cosmetic, and pharmaceutical industries. In the pharmaceutical and cosmetic industries, urea may be used in such applications as a moisturizer, transdermal drug penetration enhancer, nail treatment, and osmotic diuretic. In the automotive industry, urea may be used as an after-treatment for diesel engines. Specifically, urea is used in a selective catalytic reduction (“SCR”) process to eliminate oxides of nitrogen (“NOx”) from lean-burn and diesel engines. The SCR process involves aqueous urea as a reducing agent injected and mixed with the engine's exhaust stream and catalytically reacted with the NOx. The NOx is reduced to N2 and H2O. Ammonia alone is also used in SCR, but the use of urea and ammonia together reduces SCR performance because competing reactions hamper NOx reduction.
Urea is produced from ammonia and carbon dioxide in an equilibrium reaction with an incomplete conversion of the reactants. Once produced, urea also hydrolyzes into ammonia and other impurities. As such, urea is often found unsuitable for many applications in the different industries. To stabilize the urea, additives, such as lactone in pharmaceutical and cosmetic applications, have been used, and to remove the ammonia in urea, catalysts of zeolite, metal hydroxides and metal cation loaded media have been used.
There are other unfavorable effects with urea impurities, such as ammonia, including unpleasant odors, health concerns, EPA concerns, pressure build-up from release of gas reactants, shelf-life restrictions, disposal issues for past shelf-life inventory, and potential for corrosion.